Optical waveguides – Optical fiber waveguide with cladding – Utilizing multiple core or cladding
Reexamination Certificate
2000-04-03
2002-06-04
Ullah, Akm E. (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
Utilizing multiple core or cladding
Reexamination Certificate
active
06400880
ABSTRACT:
This invention relates to a degradable optical fiber. More precisely, the invention relates to a self-degradable optical fiber, that is to say, an optical fiber that contains, within its own structure, compounds capable of leading to its degradation.
The invention also concerns a method of preparing said fiber.
The technical field of the invention can be defined as that of optical fibers in general, and particularly optical fibers used for the guidance of various devices.
It is known that, today, optical fibers have acquired considerable importance in all industrial fields, such as telecommunications, opto-electronic components, sensors and lasers among others.
The traditional structure of an optical fiber comprises a core, a sheath surrounding this core and finally a coating or protective layer made of an organic polymer intended to protect the core silica and the optical sheath, notably from ambient humidity, and enables the fibers to preserve their mechanical properties.
The optical fibers have the advantage of being insensitive to the surrounding medium, compact and simple to manufacture.
These properties have been put to good use, particularly in the field of devices guided by wires and notably, wire guided missiles. In effect, the optical fibers have mechanical and optical properties which are very little affected by attack due to various external agents. Consequently, the optical fibers ensure stable video transmissions of good quality, so that, for example, it allows the person firing the device to observe the area being flown over by the missile and then to guide it to its target.
Hence, the optical fibers are themselves not very sensitive to electromagnetic radiation, to thermal stresses such as those caused, for example, by passage within the jet of hot gas discharged by the missile engine, and finally, the fiber is also very resistant to corrosion under stress and to chemical and physical aging.
It has proved to be the case that long term storage of optical fibers under extreme conditions of relative humidity and temperature poses no problem whatsoever and does not cause any significant degradation in its mechanical or optical properties.
Nevertheless, this excellent resistance or virtual insensitiveness of the optical fibers to electromagnetic, thermal, mechanical, chemical or any other attack met with in the natural environment which has just been described, has a number of disadvantages. In particular, in the case where the optical fiber is used to guide a device, such as a missile, after the unwinding of the optical fiber spool fitted to the missile, the fiber remains on the ground in a random fashion in relation to the geometry of accidents of the terrain, natural obstacles, vegetation and various buildings.
The presence of optical fibers of great length, the sheath of which has a high mechanical strength, may constitute a nuisance for personnel called upon to move over the terrain, possibly using various vehicles, a short time after firing the missiles. The optical fibers are also a source of potential restriction for personnel who are close to or on the firing ground.
In addition, these practically non-degradable fibers will constitute a long term source of pollution for the natural environment.
It is known to degrade used optical fibers by various mechanical and/or chemical treatments. However, such methods cannot be used on fibers of great length, spread out over a large surface area, in a natural environment, these fibers generally having to be degraded within a relatively short space of time.
Therefore, there is a requirement for an optical fiber comprising a core, an optical sheath and a coating which can be simply and rapidly degraded at the end of its use, without its previous optical or mechanical properties being affected.
In particular, there exists a need for an optical fiber, intended notably for the guidance of wired guided devices, such as missiles, the optical and mechanical properties of which are preserved during its storage and up to the end of its use, and which, under all possible climatic conditions is, at the end of this, able to self-degrade sufficiently within a defined period of time.
By degradation, one understands notably a loss of mechanical properties capable of leading to a degradation of the coating and then to the destruction or disintegration of the optical fiber.
The aim of the invention is therefore to provide an optical fiber comprising a core, an optical sheath and a coating made of an organic polymer which responds to the list of requirements mentioned above, which does not have the drawbacks, limitations, defects and disadvantages of existing optical fibers and which resolves the problems posed by these optical fibers.
This aim and others are achieved conforming to the invention by an optical fiber comprising a core, an optical sheath and a polymer coating, in which at least one calixarene is incorporated in said coating, said calixarene(s) imprisoning at least one compound capable of being released under defined conditions of temperature and/or humidity and/or irradiation and of bringing about degradation of said coating.
By degradation, one understands generally according to the invention, first and foremost, breaks spaced apart here and there on the fiber, for example, at the end of its unwinding, that is to say that the fiber no longer comprises very long strands, of a length, for example, greater than 500 m.
According to the invention, this process of degradation of the fiber, revealed by intermittent breaks in the fiber here and there, has progressed sufficiently, at the end of a desired time, for the fiber no longer to present a nuisance to personnel. This process of degradation may then progress, but more slowly, as a function of the conditions of the natural environment, possibly until the quasi-total degradation of the fiber.
According to the invention, said at least one calixarene is to be found included in the coating of the optical fiber.
Calixarenes are compounds of the oligomeric cyclic phenol type used mainly in super-molecular chemistry and in which the successive phenol rings are linked through a —CH
2
— group in the ortho position (positions 2, 5).
These compounds have excellent compatibility with all types of polymers, in particular organic polymers, such as the polymers used for the coating of the optical fiber.
In other words, calixarenes do not react with said polymers, particularly organic polymers, under their general conditions of use, which proves to be particularly important, notably in the case where the optical fiber is a fiber used for guiding missiles and other guided equipment, since then, no degradation of the polymer and therefore of the fiber occurs under the action of the calixarene, in particular under the conditions of storage.
In addition, the presence of phenol rings in the structure of the calixarenes also implies a very high thermal stability which is surprising for organic molecules.
This property is also put to good use in the invention since heating of the fiber, for example, due to the firing of the missile ought not therefore to have an impact on the properties and the effects of the calixarenes.
The calixarenes included in the coating of the optical fiber are, according to the invention chosen, preferably from among known calixarenes, comprising 4 to 10 phenol rings, preferably 4, 5, 6 or 8 phenol rings, that is to say calix[4]arene, calix[5]arene, calix[6]arene or calix[8]arene.
These calixarenes may possibly be substituted by one or more substituent groups chosen, for example, from among the linear or branched alkyl groups, alkenyl, aryl and aralkyl groups.
Preferably, said calixarene is chosen from among the calixarenes in which all the phenol rings are substituted in the para position by one and the same substituent chosen, for example, from among the linear or branched alkyl groups with from 1 to 6 carbon atoms. Preferably said alkyl group is a tert-butyl group.
The preferred calixarenes according to the invention will therefo
Donnaint Frédéric
Hebert Jean-Pierre
Aerospatiale Matra
Burns Doane , Swecker, Mathis LLP
Stahl Michael
Ullah Akm E.
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